I see this website which plots the VIIRS satellite data also accepts SQM readings, though they are rather sparse
https://www.lightpollutionmap.info/#zoom=6&lat=7401398&lon=-432104&layers=B0FFTFFFFFT
The string of readings up the M6/A74 is interesting. Perhaps I should mount a one on the roof of the car, coupled with a GPS logger.
Robin